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Spine
The vertebral artery (VA) arises from the subclavian artery, ascends in the neck to supply the posterior fossa and occipital lobes as well as provides segmental vertebral and spinal column blood supply. The VA is normally 3-5 mm in diameter and the ostium is the most common site of stenosis. The origin of the VA is usually from the posterior superior part of the subclavian arteries bilaterally, although the origin can be variable: * brachiocephalic artery (on the right) * aortic arch: 6% of cases. When the origin is from the arch, then it is common for the artery to enter the foramen transversarium at a level higher than normal (C5 instead of C6). Segments The vertebral artery is typically divided into 4 segments: * V1 (extraosseous): origin to transverse foramen of C6 . V1 angles posteriorly between longus colli medially and scalenus anterior laterally behind the common carotid artery to enter the transverse foramen of C6. Relations: ** anteriorly: common carotid artery, vertebral vein, thoracic duct (left VA) and lymphatic duct (right VA) ** posteriorly: ventral rami of C7 and C8, transverse process of C7, inferior cervical ganglion ** anteromedially: inferior thyroid artery, middle cervical ganglion * V2 (foraminal): from the transverse foramen of C6 to the transverse foramen of C2. Here it is accompanied by vertebral veins and sympathetic nerves. * V3 (extraspinal): from C2 to the dura. V3 sweeps laterally to pass through the transverse foramen of C1 (atlas). Exits top of atlas (C1) transverse foramen, lies on top of C1 ring, curving posteromedially around atlantooccipital joint. It turns sharply anterosuperiorly to pierce dura at foramen magnum * V4 (intradural): from the dura, it ascends anterior to the roots of the hypoglossal nerve (CN XII) and joins its contralateral counterpart at the lower border of the pons to form the basilar artery. Branches * V1: Segmental cervical muscular and spinal branches - passing into spinal canal via intervertebral foramina and reinforce blood supply of spine and vertebrate. * V2: meningeal/muscular/spinal branches * V3: Posterior meningeal artery * V4: ** Anterior and sometimes posterior spinal arteries ** Perforating branches to medulla ** PICA: Arises from distal VA, curves around/over tonsil, gives off perforating medullary, choroid, tonsillar, cerebellar branches Vascular Territory * ASA: Upper cervical spinal cord, inferior medulla * PSA: Dorsal spinal cord to conus medullaris * Penetrating branches: Olives, inferior cerebellar peduncle, part of medulla * PICA: Lateral medulla, choroid plexus of fourth ventricle, tonsil, inferior vermis/cerebellum Variant anatomy * asymmetry may due to hypoplasia, absence or termination into PICA of one of the vertebral arteries and is very common: ** left dominant ~45% (range 42-50%) ** right dominant ~30% (range 25-32%) ** co-dominant ~25% (range 25-26%) * failure to unite for form basilar artery * complete or partial vertebral artery duplication * vertebral artery fenestration * variable origin ** aortic arch origin of left vertebral artery: incidence ~5% (range 3.1-8.3%) ** may be the second (not first branch) of the subclavian artery ** left common carotid ** thyrocervical trunk or costocervical trunk * Branching pattern: gives off ** inferior thyroid ** superior intercostal artery ** deep cervical * ostium may have variable orientation ** cranial ~47% ** posterior ~ 45% ** caudal ~5% ** anterior ~3%